Feasibility of laser surface treatment of pearlitic and bainitic ductile irons for hot rolls |
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Authors: | A Fernández-Vicente M PellizzariJL Arias |
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Affiliation: | a Department of Materials and Manufacturing Processes, AIMEN Technological Center, Relva 27A-Torneiros, 36410 Porriño, Spain b Department of Materials Engineering and Industrial Technologies, University of Trento, Via Mesiano 77, 38050 Trento, Italy c Laser Processing Center, AIMEN Technological Center, Relva 27A-Torneiros, 36410 Porriño, Spain |
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Abstract: | The effects of laser surface treatment on the microstructure, crackability and stresses generated on laser hardened layers produced in several ductile cast iron materials were investigated. Two kinds of alloys having pearlitic (SGP) and acicular (SGA) matrix microstructures were selected. Hardened layers with thicknesses ranging from 1.5 to 2.5 mm were obtained by means of laser remelting (LSRm) or laser hardening (LSH). Thermal stresses generated upon laser processing have been estimated by a simple thermal model. For energy densities delivered onto the material at above 40 J/mm2, extensive cracking was developed in SGA and SGP irons due to the contribution of thermal stresses. By lowering the energy density, crack formation was avoided in SGP irons only. At low energy densities, crack formation is controlled by the generation of transformational stresses due to excessive austenite retention. An increase of the surface temperature or the alloying content gave rise to an increase of the retained austenite and the formation of lower bainite at the remelted zone and the heat affected zones, respectively. KC fracture toughness of Fe3C carbides embedded in pearlitic and acicular matrixes was measured by means of the nano-indentation technique. Fracture toughness of cementite in SGP irons was slightly higher than in SGA irons, which can help to reduce the crackability of LSH layers. |
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Keywords: | Ductile iron Laser Hardening Remelting Phase transformation Nanoindentation Fracture toughness |
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